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Rework global alignment computation again. Now we do round up

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alignment of globals to the preferred alignment, but only when
there is no section specified on the global (by far the common
case).

llvm-svn: 102515
This commit is contained in:
Chris Lattner 2010-04-28 19:58:07 +00:00
parent 181c86e4e7
commit 9867c1a075
5 changed files with 70 additions and 33 deletions
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9
include/llvm/CodeGen/AsmPrinter.h
View File

@ -204,12 +204,8 @@ namespace llvm {
/// EmitAlignment - Emit an alignment directive to the specified power of
/// two boundary. For example, if you pass in 3 here, you will get an 8
/// byte alignment. If a global value is specified, and if that global has
/// an explicit alignment requested, it will unconditionally override the
/// alignment request.
///
/// The algorithm is:
/// Align = NumBits;
/// if (GV && GV->hasalignment) Align = GV->getAlignment();
/// an explicit alignment requested, it will override the alignment request
/// if required for correctness.
///
void EmitAlignment(unsigned NumBits, const GlobalValue *GV = 0) const;
@ -218,7 +214,6 @@ namespace llvm {
/// it if appropriate.
void EmitBasicBlockStart(const MachineBasicBlock *MBB) const;
/// EmitGlobalConstant - Print a general LLVM constant to the .s file.
void EmitGlobalConstant(const Constant *CV, unsigned AddrSpace = 0);

56
lib/CodeGen/AsmPrinter/AsmPrinter.cpp
View File

@ -61,6 +61,35 @@ static gcp_map_type &getGCMap(void *&P) {
}
/// getGVAlignmentLog2 - Return the alignment to use for the specified global
/// value in log2 form. This rounds up to the preferred alignment if possible
/// and legal.
static unsigned getGVAlignmentLog2(const GlobalValue *GV, const TargetData &TD,
unsigned InBits = 0) {
unsigned NumBits = 0;
if (const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV))
NumBits = TD.getPreferredAlignmentLog(GVar);
// If InBits is specified, round it to it.
if (InBits > NumBits)
NumBits = InBits;
// If the GV has a specified alignment, take it into account.
if (GV->getAlignment() == 0)
return NumBits;
unsigned GVAlign = Log2_32(GV->getAlignment());
// If the GVAlign is larger than NumBits, or if we are required to obey
// NumBits because the GV has an assigned section, obey it.
if (GVAlign > NumBits || GV->hasSection())
NumBits = GVAlign;
return NumBits;
}
AsmPrinter::AsmPrinter(TargetMachine &tm, MCStreamer &Streamer)
: MachineFunctionPass(&ID),
TM(tm), MAI(tm.getMCAsmInfo()),
@ -227,16 +256,12 @@ void AsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
SectionKind GVKind = TargetLoweringObjectFile::getKindForGlobal(GV, TM);
const TargetData *TD = TM.getTargetData();
unsigned Size = TD->getTypeAllocSize(GV->getType()->getElementType());
uint64_t Size = TD->getTypeAllocSize(GV->getType()->getElementType());
// If the alignment is specified, we *must* obey it. Overaligning a global
// with a specified alignment is a prompt way to break globals emitted to
// sections and expected to be contiguous (e.g. ObjC metadata).
unsigned AlignLog;
if (unsigned GVAlign = GV->getAlignment())
AlignLog = Log2_32(GVAlign);
else
AlignLog = TD->getPreferredAlignmentLog(GV);
unsigned AlignLog = getGVAlignmentLog2(GV, *TD);
// Handle common and BSS local symbols (.lcomm).
if (GVKind.isCommon() || GVKind.isBSSLocal()) {
@ -1010,7 +1035,7 @@ bool AsmPrinter::EmitSpecialLLVMGlobal(const GlobalVariable *GV) {
unsigned Align = Log2_32(TD->getPointerPrefAlignment());
if (GV->getName() == "llvm.global_ctors") {
OutStreamer.SwitchSection(getObjFileLowering().getStaticCtorSection());
EmitAlignment(Align, 0);
EmitAlignment(Align);
EmitXXStructorList(GV->getInitializer());
if (TM.getRelocationModel() == Reloc::Static &&
@ -1024,7 +1049,7 @@ bool AsmPrinter::EmitSpecialLLVMGlobal(const GlobalVariable *GV) {
if (GV->getName() == "llvm.global_dtors") {
OutStreamer.SwitchSection(getObjFileLowering().getStaticDtorSection());
EmitAlignment(Align, 0);
EmitAlignment(Align);
EmitXXStructorList(GV->getInitializer());
if (TM.getRelocationModel() == Reloc::Static &&
@ -1153,20 +1178,13 @@ void AsmPrinter::EmitLabelOffsetDifference(const MCSymbol *Hi, uint64_t Offset,
// EmitAlignment - Emit an alignment directive to the specified power of
// two boundary. For example, if you pass in 3 here, you will get an 8
// byte alignment. If a global value is specified, and if that global has
// an explicit alignment requested, it will unconditionally override the
// alignment request. However, if ForcedAlignBits is specified, this value
// has final say: the ultimate alignment will be the max of ForcedAlignBits
// and the alignment computed with NumBits and the global.
//
// The algorithm is:
// Align = NumBits;
// if (GV && GV->hasalignment) Align = GV->getAlignment();
// an explicit alignment requested, it will override the alignment request
// if required for correctness.
//
void AsmPrinter::EmitAlignment(unsigned NumBits, const GlobalValue *GV) const {
if (GV && GV->getAlignment())
NumBits = Log2_32(GV->getAlignment());
if (GV) NumBits = getGVAlignmentLog2(GV, *TM.getTargetData(), NumBits);
if (NumBits == 0) return; // No need to emit alignment.
if (NumBits == 0) return; // 1-byte aligned: no need to emit alignment.
if (getCurrentSection()->getKind().isText())
OutStreamer.EmitCodeAlignment(1 << NumBits);

29
test/CodeGen/X86/alignment.ll
View File

@ -6,7 +6,7 @@
; CHECK: .bss
; CHECK: .globl GlobalA
; CHECK: .align 8
; CHECK: .align 16
; CHECK: GlobalA:
; CHECK: .zero 384
@ -15,4 +15,29 @@
; PR6921
@GlobalB = common global { [384 x i8] } zeroinitializer, align 8
; CHECK: .comm GlobalB,384,8
; CHECK: .comm GlobalB,384,16
@GlobalC = common global { [384 x i8] } zeroinitializer, align 2
; CHECK: .comm GlobalC,384,16
; This cannot get rounded up to the preferred alignment (16) if they have an
; explicit alignment specified *and* a section specified.
@GlobalAS = global { [384 x i8] } zeroinitializer, align 8, section "foo"
; CHECK: .globl GlobalAS
; CHECK: .align 8
; CHECK: GlobalAS:
; CHECK: .zero 384
; Common variables should not get rounded up to the preferred alignment (16) if
; they have an explicit alignment specified and a section specified.
; PR6921
@GlobalBS = common global { [384 x i8] } zeroinitializer, align 8, section "foo"
; CHECK: .comm GlobalBS,384,8
@GlobalCS = common global { [384 x i8] } zeroinitializer, align 2, section "foo"
; CHECK: .comm GlobalCS,384,2

4
test/CodeGen/X86/unaligned-load.ll
View File

@ -29,8 +29,8 @@ return:
declare void @llvm.memcpy.i64(i8* nocapture, i8* nocapture, i64, i32) nounwind
; CORE2: .section
; CORE2: .align 3
; CORE2: .align 4
; CORE2-NEXT: _.str1:
; CORE2-NEXT: .asciz "DHRYSTONE PROGRAM, SOME STRING"
; CORE2: .align 3
; CORE2: .align 4
; CORE2-NEXT: _.str3:

5
test/FrontendC/cstring-align.c
View File

@ -1,6 +1,5 @@
// RUN: %llvmgcc %s -c -Os -m32 -emit-llvm -o - | llc -march=x86 -mtriple=i386-apple-darwin10 | FileCheck %s -check-prefix=DARWIN32
// RUN: %llvmgcc %s -c -Os -m64 -emit-llvm -o - | llc -march=x86-64 -mtriple=x86_64-apple-darwin10 | FileCheck %s -check-prefix=DARWIN64
// XFAIL: *
// XTARGET: darwin
extern void func(const char *, const char *);
@ -9,10 +8,10 @@ void long_function_name() {
func("%s: the function name", __func__);
}
// DARWIN64: .align 3
// DARWIN64: .align 4
// DARWIN64: ___func__.
// DARWIN64: .asciz "long_function_name"
// DARWIN32: .align 2
// DARWIN32: .align 4
// DARWIN32: ___func__.
// DARWIN32: .asciz "long_function_name"